1. Field of the Invention
The present invention relates generally to the attachment of microlenses to an optical device, and to the production of microlenses to be attached to an optical device. More particularly, the present invention relates to an optical device having a microlens secured thereto, and to a process for producing microlenses for such use on a mass-production basis by use of a light-permissive die or stamper, hereinafter referred to as the "stamper".
2. Description of the Prior Art
In this specification, the "microlens" means a lens of a size of not larger than a few millimeters, and also means a group of such microlenses which are arranged one-dimensionally or two-dimensionally. Hereinafter, these two types are generally referred to as "microlens".
The microlens can be used for various uses, for example:
(1) To intensify luminance by focusing light in areas around picture elements in non-luminant display devices such as liquid crystal devices, as disclosed in Japanese Laid-Open Patent Publications Nos. 60-165621 to 165624, and No. 60-262131. PA1 (2) As light pick-up means such as laser disc, compact discs, and optical magnetic disc. PA1 (3) As a focusing means for coupling a luminant device or a receptive device to an optical fiber. PA1 (4) As a focusing means or an image forming means for focusing an incident light in a photoelectric converting zone so as to increase the sensitivity of a primary image sensor used in a solid-state image devices such as a CCD or facsimile machines (Japanese Laid-Open Publications Nos. 54-17620 and 57-9180). PA1 (5) As an image forming means for forming an image on a sensitive medium to be printed by a liquid crystal printer or an LED printer (Japanese Laid-Open Publication No. 63-44624, etc.). PA1 (6) As a filter for treating photoinformation. PA1 (1) A substrate containing ions is submerged in a solution of alkaline salt, and ions are exchanged between the substrate and the salt solution through a mask formed on the substrate, thereby obtaining a substrate having a distribution of indexes of refraction corresponding to the pattern of the mask ("Ion Exchange Method" Applied Optics, 21(6), page 1052 (1984), Electron Lett., 17, page 452 (1981)). PA1 (2) A photosensitive monomer is irradiated with ultra violet rays so as to polymerize an irradiated portion of the photosensitive monomer. Thus, the irradiated portion is caused to bulge into a lens configuration under an osmotic pressure occurring between the irradiated portion and the non-irradiated portion ("Process of Producing Plastic Microlenses"--24th Micro-Optics Meeting). PA1 (3) A photosensitive resin is patterned into circles, and heated to temperatures above its softening point so as to enable the peripheral portion of each circular pattern to sag by surface tension, this process being referred to the "heat sagging process", ("Heat Sagging Process" by Zoran D. Popovic et al--Applied Optics, 27 page 1281 (1988)). PA1 (4) A lens substrate is mechanically shaped into a lens (Mechanical Process).
To make microlenses, the following processes are known:
A disadvantage common to these processes is that it requires several steps, therefore takes a relatively long time. As a result, they are not suitable for mass-production.
To achieve mass-production, an injection method employing a stamper made of metal such as nickel is proposed for molding plastic material into microlenses. However, the optical device having microlenses attached by this process has a disadvantage in that the microlenses are likely to separate from the optical device because of a difference in the coefficient of expansion, when the optical device is subjected to a rise in the ambient temperature.
There is another proposal for employing a stamper whereby a microlens is directly formed on an optical device. This process requires relatively high temperature and pressure. However, if such treatment is likely to damage the optical device that is normally liable to heat and pressure.
There is a further proposal for employing a metallic stamper that is applied to a photosensitive layer formed on the optical device so as to shape a lens configuration, and then the formed lens is allowed to harden under the irradiation of ultra violet rays. Under this process the ultra violet rays cannot be radiated from the side of the stamper but must be done from the side of the optical device. To effect the radiation of ultra violet rays through the optical device, the optical device should have a sufficient porosity to allow them to pass. These considerations restrict the selection of a material of which optical devices are made.